1. Field of the Invention
The present invention relates to a waveguide-transmission line converter for converting electromagnetic energy in microwave or millimeter wave regions of the electromagnetic spectrum between a waveguide and a transmission line.
2. Description of the Related Art
Conventional waveguide-transmission line converters are known from Japanese laid-open patent publication No. 2002-359508 and Japanese laid-open patent publication No. H10-126114, for example.
The waveguide-transmission line converters disclosed in the above publications will be described below with reference to FIGS. 1(a) through 1(d) and 2(a) through 2(d) of the accompanying drawings.
FIGS. 1(a) through 1(d) show a patch-resonator waveguide-transmission line converter as disclosed in Japanese laid-open patent publication No. 2002-359508. FIG. 1(a) is a perspective view of the patch-resonator waveguide-transmission line converter, FIG. 1(b) a cross-sectional view of the patch-resonator waveguide-transmission line converter, FIG. 1(c) a plan view of the waveguide-transmission line converter, and FIG. 1(d) a bottom view of a dielectric substrate of the patch-resonator waveguide-transmission line converter.
As shown in FIGS. 1(a) through 1(d), the patch-resonator waveguide-transmission line converter has an elongate rectangular dielectric substrate J1 with a stripline J2, FIGS. 1(a)-1(c), disposed on one surface thereof, and a waveguide J3, FIGS. 1(a) & 1(b), mounted on the dielectric substrate J1 with a ground metal layer J4, FIGS. 1(b) & 1(d), interposed between the dielectric substrate J1 and the waveguide J3. The ground metal layer J4 is in the form of a centrally open rectangular frame having a width which is substantially the same as the thickness of the side walls of the waveguide J3.
The patch-resonator waveguide-transmission line converter also has a short-circuit plate J5, FIGS. 1(a)-1(c), fixedly mounted on the surface of the dielectric substrate J1 remotely from the waveguide J3. The short-circuit plate J5 has an outer profile which is substantially the same as the outer profile of the rectangular dielectric substrate J1. The short-circuit plate J5 has a recess defined centrally therein which is open at a longitudinal side edge thereof. With the short-circuit plate J5 fixedly mounted on the dielectric substrate J1, the stripline J2 is disposed in and exposed from the recess.
A matching element J6 FIG. 1(b) & 1(d) which comprises a substantially square metal layer is mounted centrally on the other surface of the dielectric substrate J1 remote from the stripline J2. The matching element J6 is spaced a predetermined distance from the stripline J2 and the short-circuit plate 5, and electromagnetically coupled to the stripline J2 across the dielectric substrate J1.
FIGS. 2(a) through 2(d) show a back-short waveguide-transmission line converter as disclosed in Japanese laid-open patent publication No. H10-126114. FIG. 2(a) is an exploded perspective view of the back-short waveguide-transmission line converter, FIG. 2(b) a cross-sectional view of the back-short waveguide-transmission line converter, FIG. 2(c) a plan view of the back-short waveguide-transmission line converter, and FIG. 2(d) a bottom view of a dielectric substrate of the back-short waveguide-transmission line converter.
As shown in FIGS. 2(a) through 2(d), the back-short waveguide-transmission line converter has a rectangular dielectric substrate J11 with a stripline J12, FIGS. 2(a)-2(c), disposed on one surface thereof, and a waveguide J1 having an opening defined in an end thereof. The dielectric substrate J11 is mounted on the open edge of the waveguide J13 is with a ground metal layer J14, FIGS. 2(a), 2(b) & 2(d), interposed between the dielectric substrate J11 and the open edge of the waveguide J13. The back-short waveguide-transmission line converter also has a short-circuit waveguide block J15, FIGS. 2(a) & 2(b) mounted on the open edge of the waveguide J13, with the dielectric substrate J11 positioned therebetween.
The conventional waveguide-transmission line converters shown in FIGS. 1(a) through 1(d) and 2(a) through 2(d) are capable of exchanging electromagnetic energy transmitted by the waveguides J3, J13 electromagnetic energy transmitted by the striplines J2, J12, respectively with each other.
Waveguide-transmission line converters should desirably be able to pass electromagnetic energy at a high ratio with minimum energy reflection in order to allow the electromagnetic energy transmitted by the waveguide and the electromagnetic energy transmitted by the transmission line to be exchanged with each other at a low energy loss.
Waveguide-transmission line converters have their electromagnetic energy passing and reflecting characteristics variable depending on the frequency of the electromagnetic energy that is converted by the waveguide-transmission line converter. If a waveguide-transmission line converter is applied to convert electromagnetic energy in the millimeter wave range, then since the electromagnetic energy has a frequency in the range from 76 to 77 GHz, for example, the waveguide-transmission line converter should desirably be able to pass electromagnetic energy at a high ratio with low energy reflection in that frequency range.
However, it has been confirmed that the conventional waveguide-transmission line converters disclosed in the above publications are problematic in that they fail to pass electromagnetic energy at a high ratio with low energy reflection due to assembling errors. This problem will be described below with reference to FIGS. 3(a), 3(b), and 4(a) through 4(d) of the accompanying drawings.
FIG. 3(a) shows in cross section the conventional waveguide-transmission line converter disclosed in Japanese laid-open patent publication No. 2002-359508, the view showing an assembling error occurring on the waveguide-transmission line converter. As shown in FIG. 3(a), the matching element J6 and the ground metal layer J4 are spaced a predetermined distance from each other. If the dielectric substrate J1 is assembled in position in exact alignment with the waveguide J3, as shown in FIG. 1(b), then since the edges of the matching element J6 are spaced a shortest distance from the edges of the ground metal layer 4, no problem arises in the propagation of electromagnetic energy. However, if the dielectric substrate J1 is assembled out of alignment with the waveguide J3, as shown in FIG. 3(a), an edge J6a of the matching element J6 is spaced a shortest distance from an upper inner corner J3a of a side wall of the waveguide J3, not from an edge J4a of the ground metal layer J4. Therefore, an electric field concentration occurs in an encircled area E in FIG. 3(a), i.e., an area including the edge J6a and the upper inner corner J3a, tending to change the electromagnetic energy passing and reflecting characteristics of the waveguide-transmission line converter.
FIG. 3(b) shows in cross section the conventional waveguide-transmission line converter disclosed in Japanese laid-open patent publication No. H10-126114, the view showing an assembling error occurring on the waveguide-transmission line converter. As shown in FIG. 3(b), the stripline J12 and the short-circuit waveguide block J15 are spaced a predetermined distance from each other. If the dielectric substrate J11 is assembled in position in exact alignment with the waveguide J13, as shown in FIG. 2(b), then since an edge of the stripline J11 is spaced a shortest distance from the inner surface of a side wall of the short-circuit waveguide block J15, no problem arises in the propagation of electromagnetic energy. However, if the dielectric substrate J11 is assembled out of alignment with the waveguide J13, as shown in FIG. 3(b), the edge J12a of the stripline J12 is spaced a shortest distance from an upper inner corner J13a of a side wall of the waveguide J13, not from an inner surface portion J15a of the side wall of the short-circuit waveguide block J15. Therefore, an electric field concentration occurs in an encircled area F in FIG. 3(b), i.e., an area including the edge J12a and the upper inner corner J13a, tending to change the electromagnetic energy passing and reflecting characteristics of the waveguide-transmission line converter. FIGS. 4(a) through 4(d) show the relationship based on experimental numerical calculations between assembling errors of the waveguide-transmission line converter disclosed in Japanese laid-open patent publication No. 2002-359508 and variations of the electromagnetic energy passing and reflecting characteristics thereof. In each of FIGS. 4(a) through 4(d), a curve plotted by interconnecting symbols Δ represents the magnitude, represented by an amplitude, of a reflected electromagnetic energy when an electromagnetic energy is transmitted from the stripline J2 to the waveguide J3, a curve plotted by interconnecting symbols ◯ represents the magnitude, represented by an amplitude, of a reflected electromagnetic energy when an electromagnetic energy is transmitted from the waveguide J3 to the stripline J2, and a curve plotted by interconnecting symbols □ represents the magnitude, represented by an amplitude of a passed electromagnetic energy when an electromagnetic energy is transmitted from the waveguide J3 to the stripline J2. FIG. 4(a) shows the relationship plotted when the dielectric substrate J1 was not displaced out of alignment with the waveguide J3, i.e., the dielectric substrate J1 was displaced out of alignment with the waveguide J3 by no displacement of aO. FIG. 4(b) shows the relationship plotted when the dielectric substrate J1 was displaced out of alignment with the waveguide J3 by a displacement of a1 which was greater than no displacement of aO. FIG. 4(c) shows the relationship plotted when the dielectric substrate J1 was displaced out of alignment with the waveguide J3 by a displacement of a2 which was greater than the displacement of a1. FIG. 4(d) shows the relationship plotted when the dielectric substrate J1 was displaced out of alignment with the waveguide J3 by a displacement of a3 which was greater than the displacement of a2.
It can be seen from FIGS. 4(a) through 4(d) that if there is no displacement between the dielectric substrate J1 and the waveguide J3, any electromagnetic energy reflection is small in the frequency range in which the waveguide-transmission line converter is used, but the magnitude of the electromagnetic energy reflection varies greatly outside of that frequency range. It can also be understood that if the dielectric substrate J1 is displaced out of alignment with and the waveguide J3, then small electromagnetic energy reflection occurs at different frequencies depending on the displacement. For example, if the dielectric substrate J1 is displaced out of alignment with the waveguide J3 by the displacement of a1, then the magnitude of any electromagnetic energy reflection in the millimeter wave range from 76 to 77 GHz is widely different from the magnitude of any electromagnetic energy reflection in the millimeter wave range that occurs if the dielectric substrate J1 is not displaced out of alignment with the waveguide J3 (see FIGS. 4(a) and 4(b)).